<!DOCTYPE html>
<html lang="en">

<head>
    <title></title>
    <meta charset="UTF-8">
    <style>
        .box {
            width: 200px;
            height: 200px;
            background: red;
        }
    </style>
</head>

<body>
    <div class="box">123</div>
</body>

</html>